I have a Xeon 2637 V3 processor in a Supermicro X10DRI-LN4+ Motherboard. I'd like to add a second 2637 but having a hard time finding a decent price on a v3. Is the 2637 v4 "socket compatible" enough to be mixed with the v3 CPU already in this board?

DeeH: Thank you very much for joining the Intel® Processors communities. We will do our best in order to provide the information you are looking for.

In regard to your inquiry, from our end, that combination will not be possible since the processors need to be exactly the same model with the same s-spec to work on a dual socket configuration. In order to gather further details about this matter, you can also get in contact with Supermicro directly:https://www.supermicro.com/support/contact.cfm